The news that a female shark at an Italian aquarium gave birth without having mated with a male first was widely reported. But how rare is a "virgin birth" in sharks?
A lack of mate could be one reason why a shark might reproduce asexuallyImage: Stefan Sauer/dpa/picture alliance
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Scientists at the Cala Gonone Aquarium on the Italian island of Sardinia say a female smooth-hound shark that's been living in an all-female shark tank for 10 years recently gave birth to a baby shark.
The aquarium's press team told DW that they are currently waiting for a DNA analysis to confirm that what happened is a case of parthenogenesis.
To procreate, most species require an egg to be fertilized by a sperm. That's the case with sharks, too. But some animals can produce offspring all by themselves. This is called parthenogenesis.
The term comes from the Greek words parthenos, meaning "virgin," and genesis, meaning "origin."
The case in Italy could be the first time this "immaculate conception" has occurred in smooth-hound sharks, at least in captivity.
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It isn't the first time parthenogenesis has been seen in sharks , and the process has been observed in a number of other shark species.
But scientists still don't know how often it happens, says Kevin Feldheim, a researcher at the Field Museum in Chicago, who researches the mating habits of sharks.
"We don't know how common it is and the handful of cases we have seen have mostly taken place in an aquarium setting," Feldheim told DW.
One study from the Field Museum discovered parthenogenesis in a wild population of smalltooth sawfish, a type of ray. This was the first time a vertebrate (animals with backbones inside their body), which usually reproduces the conventional way with a mate, was found to reproduce asexually in the wild, Feldheim said.
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Where do the babies come from?
In sharks, asexual reproduction usually happens via a process called "automictic parthenogenesis," explained Feldheim. During egg development, one egg is produced along with three other products called polar bodies.
Usually these polar bodies are simply reabsorbed by the female. Parthenogenesis occurs when one of the polar bodies has the same amount of genetic material as the egg and fertilizes it.
The year after being separated from her male mate, the older female shark didn't lay any eggs. The following year her daughter from her previous mate was added to the tank. Two years later, the mother had three pups on her own, while her daughter had one.
Scientists think the lack of a mate could be a cause for asexual reproduction.
"We think that being without a male certainly triggers parthenogenesis," said Feldheim, "but beyond that, we don't know the mechanism."
A close look at marine marvels
The ocean is truly home to some of the most amazing creatures, such as species recently discovered under Antarctica. Here's a selection of the world's most interesting aquatic animals.
Image: British Antarctic Survey/dpa/picture alliance
Unknown life
Under permanent ice cover that is hundreds of meters thick in Antarctica, researchers have discovered sessile animals (similar to sponges) that have adapted to extreme conditions like darkness and subzero temperatures, as well as being under such expanses of ice that these organisms are 260 kilometers (155 miles) from the open sea. To what species the rock-bound creatures belong remains unclear.
Image: British Antarctic Survey/dpa/picture alliance
Water dragon
It looks like a seahorse — but it's a red sea dragon, a rare marine fish. Researchers off the coast of Western Australia have only recently been able to admire these live specimens, which were identified in 2015. The animals were observed feeding at a depth of 50 meters (165 feet).
Image: picture-alliance/dpa/Scripps Oceanography/UC San Diego
Seahorses
The "real" seahorses are also quite unusual. They are one of the few species to swim vertically. But this doesn't work out too well, so they are just poor swimmers. The males carry fertilized eggs and give birth to their young.
Image: picture-alliance/ dpa
Electric eels
Despite its name, an electric eel is not an eel but a knife fish. It is indeed electric, though, and generates powerful electric shocks of up to 600 volts to kill prey. Researchers have learned that the fish also uses its high-voltage discharge as a high-precision tracking device — similar to the echolocation calls of bats.
Image: imago/Olaf Wagner
Banded archerfish
Banded archerfish live in brackish water and have come up with a unique way to kill prey: They spit a jet of water into the air to shoot down insects. Larger fish may even hit targets up to 3 meters away.
This fish buries itself in the sand and waits till its prey passes its head. Then it shoots upward and gets its meal. Stargazers have top-mounted eyes and a large, upward-facing mouth. If you ever see one, be careful: The species is venomous.
Image: picture-alliance / OKAPIA KG
Stonefish
Venomous and good at hiding? The stonefish is both! The species looks exactly like a stone overgrown with algae. But step on it and you will come to know its needlelike venomous spines. It can even be fatal for humans.
Image: gemeinfrei
Puffer fish
Puffer fish have an elastic stomach that they can fill with water when feeling threatened. This way they become much larger and almost spherical in shape. They produce the tetrodotoxin, which can kill humans. In Japan, people eat puffer fish.
Image: picture alliance/Arco Images
Anglerfish
An anglerfish attracts its prey with an illicium, or a fleshy growth from its head. The tip of the illicium illuminates to make prey curious — and then they are swallowed up by the huge mouth of the predator. Anglerfish can be found almost anywhere in the world, including the deep sea.
Image: Flickr/Stephen Childs
Viperfish
With high pressure, almost no light and little food, animals have to be especially adapted to be able to live in the deep sea. Viperfish need to make absolutely sure that they don't miss a meal — that's what the huge mouth and the sharp teeth are for.
Image: picture-alliance/dpa
Plaice
The plaice is a flatfish — no doubt about that. The well-camouflaged fish bury themselves in the sediment. They develop so that both eyes end up on the same side of the head.
Image: picture-alliance/dpa/H.Bäsemann
Mudskippers
Mudskippers apparently couldn't decide whether they liked land or water more. So they compromised and chose intertidal habitats. They are definitely fish but can use their pectoral fins to walk on land. They can breathe through their skin like amphibians.
Image: picture-alliance/dpa/MAXPPP
Hammerhead shark
Researchers believe that the flat, sideways extended head gives hammerhead sharks a higher visual field. That helps them find their prey.
